You need a good war or a step change in naval technology to increase demand
Artillery is good generally but can be glutted.
Generally the war industries don't make alot of money until after cheap coal / iron / steel and the Colt efficiency upgrade. And even then you need decent railways.
Trouble is that sulphur is in short supply which means its expensive and steel is in high demand (railways etc) which means that its expensive too. You can play around with this in 1.02 by adjusting factory inputs in the economy files of the db folder. In 1.03 you can play with the factory (and RGO) outputs as well.
Building a fertiliser factory as a discretionary build with prussia early on is a bad move unless you can acquire Anhalt (I think) with a sulphur source or maintain high prestige. Better to follow the advice given in this thread. Of course you do need to keep reserves of war materiel but these can be bought.